Recent developments in controlled radical polymerization have demonstrated the advantage of polyalkoxyamines, as described in Accounts of Chemical Research, 1997, 30, pages 373–382.
These polyalkoxyamines, under the effect of heat, in the presence of an olefin which can be polymerized by the radical route, initiate the polymerization while making it possible to control it.
The mechanism of this control can be represented diagrammatically as follows:
with M representing a polymerizable olefin and P the growing polymer chain.
The key to the control is related to the constants kdeact, kact and kp (T. Fukuda and A. Goto, Macromolecules 1999, 32, pages 618 to 623). If the ratio kdeact/kact is too high, the polymerization is blocked, whereas, when the ratio kp/kdeact is too high or when the ratio kdeact/kact is too low, the polymerization is not controlled.
P. Tordo et al., Polym. Prep. 1997, 38, pages 729 and 730, and C. J. Hawker et al., Polym. Mater. Sci. Eng., 1999, 80, pages 90 and 91, have found that β-substituted alkoxyamines make it possible to efficiently initiate and control the polymerization of several types of monomers, whereas the alkoxyamines derived from TEMPO [such as (2′,2′,6′,6-tetramethyl-1′-piperidnyloxy)methylbenzene, mentioned in Macromolecules, 1996, 29, pages 5245–5254] control, under conditions which can be operated industrially, only the polymerizations of styrene derivatives.
In U.S. Pat. No. 6,657,043, the polyalkoxyamines make it possible to synthesize polymers and copolymers with well-defined architectures. For n=2 (dialkoxyamine), it is possible to synthesize triblock copolymers, each block resulting from monomers as different as alkyl acrylates and/or styrene derivatives, with excellent control of the polymerization and of the polydispersity and with very short polymerization reaction times.
Thus, for example, it is possible to successively polymerize two monomers M1 and M2:

By way of example, M1=alkyl acrylate and M2=styrene.
Starting from trialkoxyamine (n=3), “star” polymers will be obtained.
The polyalkoxyamines can be synthesized by different methods. One method involves the reaction of a halogenated derivative A(X)n in the presence of an organometallic system, such as CuX/ligand (X=Cl or Br), according to a reaction of ATRA (Atom Transfer Radical Addition) type as described by D. Greszta et al. in Macromolecules, 1996, 29, 7661–7670. A process of this type is disclosed in U.S. Pat. No. 6,657,043 on behalf of the Applicant Company. Another method involves the reaction of a functional alkoxyamine, for example carrying an alcohol functional group, with a polyacid or a poly(acid chloride), as described, for example, by C. J. Hawker in Accounts of Chemical Research 1997, 30, 373–382. These methods exhibit the disadvantage of using reactants which have to be synthesized in one or more stages (polyhalogenated compounds, functional alkoxyamines) and of requiring relatively complex purification stages. Furthermore, the intermediates in these syntheses may be novel products which require developments and adaptations and/or modifications, indeed even complete replacement, of the industrial equipment, which is not favourable to the use of such syntheses on the industrial scale.
C. J. Hawker has also described, in Accounts of Chemical Research 1997, 30, 373–382, the preparation of a polyalkoxyamine by oligomerization of a functional alkoxyamine carrying a styrene double bond. However, the fact that the thermal stabilities of the polyalkoxyamine and of the starting alkoxyamine are equivalent makes it very difficult to control the synthesis of the polyalkoxyamine due to the concomitant formation of gels. Thus, the preparation of polyfunctional living polymers has also been envisaged by addition of a monofunctional living polymer to polyfunctional vinylbenzenes (see, for example, P. Chaumont in Macromolecules (2001), 34(12), 4109–4113) but, on proceeding in this way, the author has characterized products which are gelled as a result of the crosslinking.